The objectives of this project are two-fold: 1) to elucidate the role of conformational changes, segmental flexibility, and domain interactions in the moleucular mechanisms of antigen induced effector activation in immunoglobulins, and 2) to study the tertiary structure of the combining site of the IgM myeloma protein produced by the murine cell line ABPC 22. These problems will be investigated primarily by means of nanosecond fluorescence, gamma ray perturbed angular correlation spectroscopy, and circular dichroism. Our specific aims for the project period are to: 1) determine the role of the C-micron-2 domains of IgM in the transfer of information from the antibody combining site on Fab to the Cl binding site in C-micron-4; 2) to measure the segmental flexibility of cell bound antigen receptor and to determine the role (if any) of conformational changes in B lymphocyte triggering; 3) to determine the antigen specificity of ABPC 22 myeloma protein and eventually the structure of the combining site.